1. Field of the Invention
The present invention relates to a method of allocating a bandwidth of a passive optical network that can dynamically allocate a bandwidth necessary for transmitting data to an uplink or a downlink between an optical line termination and an optical network terminal in the passive optical network.
This work was supported by the IT R & D program of MIC/IITA [2007-S-014-01, “Metro-Access Integrated Optical Network Technology”].
2. Description of the Related Art
As an optical line termination (hereinafter, referred to as ‘OLT’) and a plurality of optical network terminals (hereinafter, referred to as ‘ONT’) are connected, a passive optical network (hereinafter, referred to as ‘PON’) has an ONT structure for forming distribution topology of a tree structure.
Time division multiple access (TDMA)-PON can use a cheap optical element of a single wavelength and has a structure in which several ONTs share one wavelength. Accordingly, the TDMA-PON has an advantage in a broadcasting service such as a high-definition internet protocol television (IPTV) in downward transmission and has an advantage of statistical multiplexing according to a request band of ONTs in upward transmission.
However, because the TDMA-PON originally uses each of an upward wavelength and a downward wavelength, the TDMA-PON has low efficiency of an optical link and it is difficult for the TDMA-PON to divide and use one optical fiber into several subscribers because power loss increases according to the quantity by which an optical power distributor is divided.
Because wavelength division multiplexing (WDM)-PON uses a wavelength per subscriber using a conventional method, a service band of a subscriber is sufficient, and because an optical link is used with several wavelengths, the WDM-PON has an advantage of maximizing efficiency of an optical link. However, the WDM-PON has an inflexible and static structure in which an optical element cost due to wavelength multiplexing is relatively higher than that of the TDMA-PON and in which subscribers cannot statistically share and use a band. Nevertheless, so far, the WDM-PON is regarded as a final solution that can be applied to an optical network after the TDMA-PON.
However, although the speed of the optical link gradually increases from 1 G to 10 G or 100 G, a band requested by a subscriber is sustained in a speed of less than 100 Mbps. This is because a killer application for surely upgrading the service does not exist. Therefore, at a current time point, a method in which several ONTs can share one optical wavelength by gradually combining a statistical multiplexing method of the TDM-PON to construction of a WDM-PON network than to construct only the WDM-PON network, is requested.
In an existing TDMA-PON, a broadcast method is used with a single wavelength in downward transmission and an uplink signal is received in a burst mode using a TDMA method of ONTs in upward transmission. However, in a wavelength synchronous hybrid PON, in downward transmission, because a wavelength is varied and transmitted without using a single wavelength, data should be transmitted in a burst mode in even a downlink and thus scheduling of a wavelength is necessary. In upward transmission, because a reflective semiconductor optical amplifier (RSOA) method is used, a method of allocating an upward band of an ONT for transmitting upward data within a downward wavelength band is requested.